1. Field of the Invention
The present invention relates to an RFID (Radio Frequency Identification) tag performing non-contact information exchange with outside apparatuses, an electronic component used to fabricate the RFID tag, and an RFID tag fabrication method of fabricating the RFID tag. It is noted that, among those skilled in the technical field of the present invention, “RFID tag”, as used in the present specification, is sometimes referred to as “RFID tag inlay”, which means an internal constituent member (inlay) for “RFID tag”. Alternatively, this “RFID tag” is sometimes also referred to as “wireless IC tag”. This “RFID tag” also includes non-contact IC cards.
2. Description of the Related Art
In recent years, various types of RFID tags have been proposed which perform, by radio wave, non-contact information exchange with outside apparatuses represented by a reader/writer. As one type of this RFID tag, an RFID tag has been proposed which includes an antenna pattern for radio communication and an IC chip mounted on the base sheet made of plastic, paper or the like. An application for the RFID tag of this type has been devised in which the RFID tag is attached to an article to exchange the information about the article with outside apparatuses, whereby the article is identified.
FIG. 1 is a front view (A) and a side sectional view (B) showing an exemplary RFID tag.
Referring to FIG. 1, an RFID tag 1 includes an antenna 12 disposed on a base 13 made of a sheet-like PET film or the like, an IC chip 11 connected to the antenna 12 via a bump 16, and a cover sheet 14 attached to the base 13 with an adhesive 15 so as to cover the antenna 12 and IC chip 11.
The IC chip 11 constituting the RFID tag 1 can perform radio communication with outside apparatuses via the antenna 12 to exchange information.
With this RFID tag, a wide range of applications including the foregoing one has been devised. However, fabrication cost poses one of the major problems in using this RFID tag in various applications. Thus various attempts have been made to reduce the fabrication cost.
As an attempt to reduce the fabrication cost, there has been devised a technique of forming the antenna by use of printing technology by using a paste of resin material, such as epoxy, mixed with metallic filler (typically, Ag) so as to have conductivity (for example, refer to Japanese Patent Laid-Open Nos. 2000-311226 (paragraph number [0066]), 2000-200332 (paragraph numbers [0027] and [0028]), and 2001-351082 (paragraph number [0021]). Conventionally, as a material to form an antenna, a metallic thin material such as Cu, Al, Au, or the like is used. If the above-mentioned paste material to form an antenna can be used, the fabrication cost of RFID tag can be greatly reduced.
FIG. 1 is a top view (A) and a side view (B) showing an exemplary typical configuration of the RFID tag. In the top view, part of the constituent elements is omitted; in the side view, the internal structure seen through from the side face of the RFID tag is illustrated. Hereinafter, all diagrams referred to as “top view” or “side view” in the present specification are similar to the above described diagrams.
The RFID tag 1 having a typical structure includes the antenna pattern 12 disposed on the base sheet 13 made of a PET material or the like, the IC chip 11 connected to the antenna pattern 12 via the bump 16 (metallic protrusion), the cover sheet 14 attached to the base sheet 13 with the adhesive 15 so as to cover the antenna pattern 12 and IC chip 11.
In fabricating the RFID tag 1 shown in FIG. 1, the IC chip 11 is connected, via the bump 16 formed on the IC chip 11, onto the antenna pattern 12 formed on the surface of the base sheet 13. When the antenna pattern 12 is formed by printing a paste material, the following problem may arise in performing the connection.
FIG. 2 is a conceptual diagram that explains the problem which arises when a paste is used as the antenna material.
To fabricate the RFID tag, firstly the antenna pattern 12 made of a paste material is formed on the base sheet 13 of PET material by use of a printing technique (part (A)). Subsequently, the IC chip 11 having the bump 16 formed on an electrode 111 is arranged on the base sheet 13 having formed thereon the antenna pattern 12, with the bump 16 oriented toward the base sheet 13 side (part (B)). Then, when the IC chip 11 is pressed from above in the drawing by a jig (not shown), the bump 16 provides suppress strength to the antenna pattern 12, thereby connecting the IC chip 11 to the antenna pattern 12.
At this time, a projection 12a of the paste material constituting the antenna pattern 12 is formed around the bump 16 by the suppress strength applied to the antenna pattern 12 by the bump 16. Consequently, an insulating distance required between the IC chip 11 and antenna pattern 12 can not be secured. Thus, performances achieved by the RFID tag (hereinafter, referred to as “tag performance”), such as radio communication performance, will change, causing the variations of tag performance observed when many RFID tags are fabricated.
Apart from RFID tags, it is a common practice for various types of IC chips to be mounted on a circuit board. In this case, since many bumps are formed in the IC chip, even if a paste material is employed as the wiring material on the circuit board, suppress strength per bump is small, so the projection of the paste material hardly poses any problem.
In contrast, with the RFID tag, the number of bumps used to connect the IC chip to the antenna pattern is on the order of 2 to 4 per IC chip; therefore, the suppress strength per bump is significantly large, causing the problem of the paste material being projected as described above. To reduce this suppress strength, the suppress strength applied by a device used to dispose the IC chip onto the base must be considerably reduced relative to when an ordinary IC chip having formed therein many bumps is disposed. However, with the adhesive sandwiched between the base and IC chip, it is difficult to perform rapid and highly reliable connection while considerably reducing the suppress strength.
To address the above problem, the present invention provides an RFID tag in which a paste is employed as the antenna material and at the same time, the problem of the change of tag performance caused by the above mentioned projection is avoided, a module component for use in the RFID tag, and a fabrication method of the RFID tag.